1-4 can be learned by anyone willing to read enough papers in a great, great many fields. The math needed to understand the articles in the Quarterly Journal of

1-4 can be learned by anyone willing to read enough papers in a great, great many fields. The math needed to understand the articles in the Quarterly Journal of Economics or the American Political Science review is in most cases well within reach for the population of potential applicants for a doctorate. There’s an enormous amount of valuable non-procedural knowledge that most doctoral degree holders have and most non-holders don’t but the average doctor, lawyer or senior civil servant does research that would be impossible without skills 1-4 without ever doing a Ph.D.